Manufacture of asbestos products



June 10, 1969 R N ET AL 3,449,230

MANUFACTURE OF ASBESTOS PRODUCTS Filed Nov. 8, 1966 Sheet of 2 s 5 s i g5 lumuunumwl i 5 i 50/ June 10, 1969 G. F. HERON ET AL MANUFACTURE OFASBESTOS PRODUCTS orz Sheet Filed NOV. 8, 1966 United States Patent3,449,230 MANUFACTURE OF ASBESTOS PRODUCTS Gordon F. Heron and JohnOutram Halstead, Rochdale,

England, assignors to Turner Brothers Asbestos Company Limited,Manchester, England, a British company Filed Nov. 8, 1966, Ser. No.592,941 Int. Cl. B01d 13/02 US. Cl. 204-180 Claims This inventionrelates to the manufacture of asbestos articles, that is to say,articles composed essentially of or containing asbestos. The inventionis based on the phenomenon of electrophoresis, which involves thepassage of a direct current through a dispersion of electrically chargedparticles between two electrodes, the particles being electricallyattracted towards the oppositely charged electrode so that they movetowards it and deposit on it.

It is known that if a dispersion is to be subjected to electrophoresisit must contain very highly dispersed particles. These particles aresaid to be colloidally dispersed, since one of the properties ofcolloidally dispersed particles is that they are charged and that,accordingly, they may undergo electrophoresis. It is also known that ofthe three most common types of asbestos, namely chrysotile, amosite andcrocidolite, chrysotile can readily be dispersed colloidally in waterwith an anionic dispersing agent. In the invention anionic dispersionsof asbestos are used and they may contain some noncolloidally dispersedasbestos fibres and they may even contain other constituents, eithercolloidally dispersed or merely intimately mixed, which are notasbestos. The necessary property a dispersion must possess to be usablein the invention in response to electrophoresis is that asbestos fibrein it will be electrically at tracted to an electrode when a current ispassed through the dispersion. Whether any given dispersion has thisproperty is readily ascertainable by test.

Chrysotile asbestos is sold in various grades and all grades can becolloidally dispersed.

Fibres of dry chrysotile asbestos are positively charged but when thefibres are opened and dispersed in water by means of anionic dispersingagents (e.g., soaps) their surfaces become negatively charged (due toadsorption of a layer of negative soap anions). Under the influence of adirect current, therefore, the fibres then move towards the anode.

According to the invention the dispersion is passed between twoelectrodes across which an electric potential difference is applied,whereby constituents are caused to migrate towards the anode, themigrating constituents are collected as a deposit on the anode or on anion-permeable membrane interposed in their path to the anode, and thedeposit is continuously removed from the remainder of the dispersion.Products which may be produced in this way include sheets, tapes andyarns, membranes, such as glass, cloth, coated or impregnated withabestos, and wire and other electrically conducting surfaces coated withasbestos.

It is necessary to pass the dispersion between the electrodes while theprocess is carried out since if this is not done localised electrolyticeffects occurring around the electrodes will interfere with satisfactorydeposition of asbestos.

The invention may be carried out in numerous ways. Particularlyadvantageously the deposit is continuously stripped off the anode as acoherent body. We have surprisingly found that it is possible to producedeposits of such high wet strength that the deposit can be stripped offthe anode while it is still immersed in the dispersion. However, thedeposit may be carried out of the dispersion on the anode or membraneand then either left in position to form a permanent coating on theelectrode or membrane or stripped off. I

3,449,230- Patented June 10, 1969 When the deposit is drawn off theanode or membrane while wet, high wet strength is an extremely importantproperty. For highest wet strength, long fibres should be used.Moreover, we have found that to impart high wet strength it is necessaryto deposit a binder with the asbestos. This binder is not required fordry strength in the final product, as is shown by the fact that aproduct made with it maintains its strength on removal by solventextraction or by heating to 450 C. of the organic matter in it. Thissuggests that the very fine, highly opened asbestos fibrils may begiving dry strength to the product by random arrangement andentanglement, a theory which is supported by electron microscopicexamination of the deposits.

We find that the fibres are oriented in the direction in which thedispersion flows, and in particular any incompletely opened bundles aredeposited parallel to one another. This fact accounts for an observedlarge difference in strength of electrodeposited asbestos products indirections at right angles to one another. Strengths are much higher inthe direction of drawing of continuously deposited materials and thecoarse fibres are seen to be aligned in this direction. Alignment isapparently not merely a result of the drawing or flowing motions sincealignment occurs in static deposition.

To produce the binder required for high wet strength, we use awater-soluble soap as an anionic dispersing agent. During theelectrophoresis process, electrolysis and electroosmosis occur, theelectrolysis resulting in the release of cations at the anode and abuild-up of acidity there. If the anode does not corrode during theprocess free fatty acids are formed by reaction of the resultant acidwith the water-soluble soap, and these improve the wet strength. Muchbetter wet strength is obtained by a further important feature of theinvention, namely the use as the 'anode of a metal which will corrodeduring the process as a result of electrolytic action. Ions dissolvedfrom such an anode react with the water-soluble soap to yield awater-insoluble soap which acts as a binder. The preferred metals foruse as the anode are aluminum and zinc, but copper, lead or iron mayalso be used.

When high wet strength is not important the electrode can satisfactorilybe of materials, for example platinum or carbon, which do not corrode togive ions that form insoluble soaps.

Although the water-soluble soaps serve both as dispersing agents andbinder-formers, they do not give wholly satisfactory dispersions whenused as the sole dispersing agents. To form the best dispersion and getthe highest wet strength, we prefer to use a mixture of soap and anotheranionic surface-active dispersing agent, for example an alkyl-arylsulphonate, an alkyl sulphosuccinate or a sulphated higher alcohol. Wefind a very suitable mixture to be one of 6 parts soap to 1 part of theother anionic dispersing agent. Unless otherwise specified, all partsand percentages quoted in this specification are by weight. Two examplesof dispersions which are responsive to electrophoresis are as follows:

EXAMPLE 1 Parts Tap water of hardness of about ppm. ex-

pressed as calcium carbonate (at 60 C.) 1,000 Chrysotile asbestos(Canadian Cassiar A35, length approximately 0.30") Sodium dodecylbenzene sulphonate 1.2 Soap (sodium salts of mixed long-chain fattyacids) 7 If this dispersion is used with an anode of aluminum, zinc orcopper the wet strength is good. Equal dry strength may be obtained ifthe anode is of carbon or platinum.

EXAMPLE 2 The dispersion contains 2% chrysotil asbestos fibre (SouthAfrican C and G3, length approximately 0.18") and 0.3% sodium dioctylsulphosuccinate. This dispersion can be deposited on a corrodible ornoncorrodible anode, and it requires support until it is dry. Itpresents the advantage that it yields a deposit containing only aboutorganic matter.

The proportion of the fibre in the dispersion is small, though it mayadvantageously depend on-the fibre length. With long fibres such asCanadian Cassiar A35 the propor tion in the dispersion may be from 0.5to 5%. With very short fibres such as Canadian Bells F7M (length approximately 0.0 the proportion may be as high as and preferably is at least1% There is an optimum pH of the dispersion for each anode material, soit may be necessary to adjust the pH of the dispersions of Examples 1and 2 to obtain satisfactory deposition with some anodes;

The dispersion need not consist solely of asbestos fibres, but ratherone or more constituents having the same electric charge as thedispersed fibres may also be present in the dispersion, these materialsthus undergoing electrophoresis with the asbestos fibres. In particular,the dispersion may contain both chrysotile asbestos fibres and particlesof a polymeric material. The proportion of the polymer particles mayvary from a very small to a substantial figure.

Particularly useful products, e.g., gaskets, may be made by thecodeposition of asbestos and a styrene-butadiene rubber orpolytetrafluorethylene. Other useful reinforced polymer compositions maybe made by the codeposition of asbestos and a thermoplastic,thermosetting or rubber polymer, examples of suitable polymers beingstyrene rubbers, copolymers of acrylonitrile and butadiene, copolymersof carboxylic butadiene and acrylonitrile, polyvinyl chloride,polyethylene, polystyrene, polyester resins and various mixtures ofthese.

Some examples of dispersions which contain polymer particles and areresponsive to electrophoresis are as follows:

EXAMPLE 3 The dispersion contains by weight:

2% chrysotile asbestos fibre (Canadian Cassiar A35), 2 /2 polyvinylchloride added as latex,

0.8% soap,

0.12% sodium dodecyl benzene sulphonate.

This dispersion will give a deposit containing about 34% asbestos, 57%polyvinyl chloride and 9% soap products.

EXAMPLE 4 An equivalent amount of polytetrafluoroethylene is substitutedfor the polyvinyl chloride in Example 3, and a product of low wetstrength but good dry strength is obtained. This deposit must thereforebe carried out of the dispersion on a continuous anode or other support.

EXAMPLE 5 The dispersion contains by weight:

5% chrysotile asbestos fibre (Canadian Bells C5R, length approximately0.06),

% polytetrafluoroethylene (added as a dispersion),

0.5% sodium dioctyl sulphosuccinate.

The dispersion gives deposits containing about 35% asbestos, 63%polytetrafiuoroethylene and 2% other organic matter. These deposits areuseful as gasket materials. From this dispersion a deposit of good drystrength but low wet strength is obtained, and the deposit musttherefore be carried out of the dispersion on a continuous anode orother support.

The dispersions have a surprisingly high tolerance for charged oruncharged particles and fibes, which may themselves be able to undergoelectrophoresis or which may be deposited simply by being mechanicallyentrained by the deposited fibres. Examples of colloidally dispersibleparticles which can be added are bentonite, clay, colloidal silica andgraphite. Bentonite will also act as a dispersing agent, though it doesnot produce a satisfactory colloidal dispersion without anotherdispersing agent. One example is as follows:

EXAMPLE 6 The dispersion contains by weight:

4% bentonite, 3% chrysotile asbestos fibre, 0.15% sodium dioctylsulphosuccinate.

This dispersion gives a deposit having a low wet strength.

When graphite is colloidally dispersed with the asbestos the product isgraphitised asbestos. Such products are known, but when they are made byimpregnation the graphite is largely concentrated at the surface,whereas in the product made by the invention it is uniformly dispersedthroughout the product. As an example, 20 parts of graphite by weight inthe form of a colloidal dispersion may be added to the dispersion ofExample 1.

The mechanical entrainment of uncharged constituents is surprising. Forexample, 20 parts by weight of glass fibres as chopped roving A inchlong may be added to the dispersion of Example 1. Broadly, examples ofconstituents which may be entrained by colloidally dispersed fibres thatmigrate under electrophoresis are glass fibres (as chopped roving), slagwool and noncolloidally dispersed asbestos fibres, such as fibres ofamosite or crocidolite or even of chrysotile.

In order to prevent contamination of the dispersion by bubbles of gasevolved at the cathode it is often preferable to cover the cathode by amembrane, for example a nylon cloth, which is permeable to ions but notto gas bubbles. This cathode membrane separates the liquid around thecathode from the rest of the dispersion between the electrodes.

The shape of the anode on which the deposit is formed depends on therequired product. It may be a plate of the width desired for a sheet ortape of asbestos. In order to facilitate drawing of the product off theelectrode it is desirable that deposition should occur only on theelectrode surface having the shape of the desired product and in orderto prevent extraneous deposition the other surfaces are generallyshielded. For example, an electrode for the production of sheet or tapemay be sunk in a recess in the surface of a larger nonconducting sheet,and the whole then machined to present a fiat surface. Alternatively abacking of nonconducting material may be provided on a very thinelectrode, a suitable nonconducting material being polymethylmethacrylate. However, if the plate has two conducting fiat surfaces andis located between two cathodes or within an encircling cathode, sheetor tape can be produced on both surfaces simultaneously.

A particularly suitable anode is a rotary cylinder.

If the deposit does not have sufiicient wet strength to be drawn offwithout breaking, it may be formed on a flexible band, which may be amembrane that moves over the face of the anode, for instance round arotary anode, or which may be of metal and thus constitutes the anode.

The invention is useful in the production of yarn. This may easily bemade by twisting tape made either in tape form or by slitting widersheets.

Once the wet deposit has been removed from the dispersion it is notgenerally necessary to subject it to any special treatment if it has ahigh wet strength, since strength will be maintained on drying. Thedrying may occur naturally in air, even when the deposit is rolled up,or it may be forced by heating. Similarly no special treatment isnecessary if the deposit is to form a permanent coating on an electrodeor membrane. If, however, it has low wet strength it is preferablyheated to dry it on leaving the dispersion.

Four apparatus which may be used in carrying out the invention are showndiagrammatically in FIGURES 1 to 4 of the accompanying drawings, each ofwhich shows one apparatus.

In the apparatus shown in FIGURE 1 a box-like container 1 is formed froman aluminum anode 2 and an aluminium cathode 3 separated by insulatingblocks 4 and 5. The base of the container thus formed is constituted bya block 6 having a central cavity 7 into which an inlet tube 8 leads andfrom which a series of passages 9 run to the interior of the container.The cavity in this block is closed by a door 10 which can be removed inorder to clean the cavity.

At the upper edge the cathode is shaped to form an overflow weir 11, andthe anode is similarly shaped to form an overflow weir 11, and the anodeis similarly shaped to form an overflow weir 12. Terminals 13- and 14are provided for the electrical connections to the anode and thecathode.

In operation the dispersion is pumped through the inlet tube, risesthrough the passages into the container and flows up between the anodeand the cathode, asbestos being deposited on the anode. As soon as thedeposit, shown at 15, is thick enough to handle, the upper edge islifted by hand and drawn upwards over a roller 16 and under a rubberwiper 17. From the roller 16 this deposit is taken beneath a roller 18and wrapped round it. The roller 18 is frictionally driven by engagementwith a positively driven roller 19, and is carried in bearings 20 whichare free to rise as the thickness of the sheet wound round it increases,so that at all times the surface speed of the sheet drawn away from theanode remains constant. Dispersion flows over the weir 11 and acid flowsover the weir 12.

If the dispersion of Example 1 is passed through the apparatus shown inFIGURE 1, the anode being 8 inches long, and 100 volts-DC are appliedacross the electrodes to give a current of about 8 amperes, an anodicdeposit may be withdrawn at a rate of 5 feet per minute to give a paperwhich is from 0.0015 to 0.002 inch thick after drying. The tensilestrength of a specimen of this paper measured in the direction ofmovement of the paper was found to be 5 lb. per inch of width.

It will be realised that a layer of acidic liquid is being continuouslyformed between the deposit and the anode. If this acid is permitted toenter the body of the dispersion between the electrodes it will reactwith the dispersion and form clots, which are found seriously tointerfere with satisfactory operation. It is highly desirable to preventthe acid from escaping from between the deposit and the anode, and thisis in effect done by the deposit itself, the edges of which in contactwith the insulating blocks 4 and 5 form an acid seal.

In the apparatus, shown in FIGURE 2, a cylindrical anode 72 having enddiscs 73 of insulating material is rotatably mounted within an open box74 over a trough formed by a curved cathode 75. An inlet trough 76extends across the top of the box immediately above one edge 85 of thecathode, and contains an inclined baflle 78 above an inlet 77.Dispersion supplied to the inlet 77 at a uniform rate flows round thelower edge of the baflle 78 and then over the baflle and a weir 87formed by the edge of this bafile through the gap between the anode andthe cathode. Qllll'lt is supplied to the anode through bearings 79having electrical connections, and to the cathode by a contact '80, andsome of the asbestos present in dispersion between the anode and cathodeis deposited as a sheet 81 on the anode while excess dispersion flowsover a weir 82 formed by the edge of the cathode and down a chute 83.Once an appreciable deposit has formed on the anode its end can bepicked off and the deposit drawn slowly upwards. Thereafter the sheetdeposit is continuously slowly drawn upwards, this movement causing theanode to rotate and so to present continuously fresh surface to thedispersion. Acid forming in the V- shaped between the upwardly movingdeposit and the anode is permitted to flow around the edges of thedeposit into the excess dispersion flowing over the weir 82.

Any clots adhering to the deposit should be broken oif, and it may bedesirable to trim off the edges and feed them back into the reservoir ofdispersion.

It is advantageous to cover the cathode by a membrane 84 of nylon clothwhich is permeable to ions but not to gas bubbles. This preventscontamination of the dispersion by evolved gas. Cathode liquid, formedbetween the membrane and the cathode and containing bubbles of the gas,flows axially off each end of the cathode into the box 74 and leavesthrough an outlet 86. This cathode liquid is alkaline and advantageouslyshould not reenter the dispersion.

As an example, in an apparatus as shown in FIGURE 2 the anode 72 wasapproximately 7 inches wide and there was a half-inch space between ,theanode and the cathode membrane 84. The total initial volume of adispersion of Example 1 in the reservoir and in circulation wasapproximately 30 litres, the dispersion also containing a sufficientamount, approximately 55 grams, of a mixture of 65 parts oleic acid and35 parts stearic acid to give the dispersion a pH in the range of 8.5 to8.7, this pH being the most suitable for the anode, which was of zinc. Acurrent of 5 amps at between 15 and 20 volts DC was applied between theanode and cathode and dispersion was continuously pumped in through theinlet 77 and excess dispersion flowed over the weir 82 back into thereservoir 21. A deposit of wet asbestos paper was formed on the anodeand was drawn oft, squeezed to remove excess acidic liquor and thendried. This liquor was returned to the dispersion in the reservoir tankto assist in pH control. After about 20 minutes it was seen by eye thatthe appearance of the dispersion in the reservoir was changing, andreplenishment was started. This replenishment was effected by addingundispersed asbestos fibres, oleic acid and stearic acid, soap, andsodium dodecyl benzene sulphonate as necessary. The process was runcontinuously for 42 hours, during which time approximately 125 litres ofdispersion were added to maintain the level of dispersion in thereservoir tank (ie, 125 litres of dispersion were actually used fordeposition.) Approximately 65 litres of cathode liquid were collectedand 16 litres of acidic liquid were squeezed from the paper duringwinding. 3,500 grams of dry paper (0.004 thick) were produced,containing (when dried to 1% moisture content) from 20 to 25% organicmatter. This represents deposition of the asbestos in the dispersion.

If the deposit does not have adequate wet strength, then a carrier,which may be an ion-permeable membrane, for example of fine-mesh nyloncloth, is run round the rotary anode and the deposit forms on it and caneither be left on it or stripped from it after drying as desired.Alternatively, as shown diagrammatically in FIGURE 3, the anode isreplaced by a positively driven roller 64 of insulating material, aroundwhich a continuous flexible metal band 65 passes. This band also passesround a roller 66, through a drying box 67 and round another roller 68.The deposit is formed on the band 65, and after being dried in the box67 is stripped off as shown at 69 and wound into a coil 70. It will beappreciated that in this case the band 65 is itself the anode, andcurrent is supplied to it through a carbon brush 71.

FIGURE 4 shows an apparatus in which a copper wire 50 is continuouslycoated with asbestos to form a permanent covering. The wire 50 is drawnfrom a reel 51 through a guide 52 past a contact 53' electricallyconnected so that the wire becomes the anode. The wire travels onwardspast a guide 54 into a pot 55. This pot has a base 56 of waxed cork,through which the wire 50 passes, and its body is made of plastic linedby aluminum foil 57, which forms the cathode and to which an electricalcon- 7 nection 58 is taken. The pot 53 has an inlet 59 and outlet 60 forthe dispersion, which thus flows in countercurrent to the Wire. Thecoated wire emerges from the top and is passed through a tubular wipingdevice 61 and a drying box 62 to be wound into a coil 63.

A suitable dispersion for use in coating wire as shown in FIGURE 4contains 3% chrysotile asbestos fibres (South African ,HVL4, lengthapproximately 0.10"), 0.75% soap, and 0.12% alkyl aryl sulphonate.

An apparatus similar to that shown in FIGURE 4 may also be used forforming yarn from a paper strip coated with graphite, which constitutesthe moving anode. Very short fibres of asbestos can be used to form adeposit on this strip, and the paper coated with asbestos may be twistedto form the yarn.

We claim:

1. A process for the production of an asbestos product comprising thesteps of passing an anionic aqueous dispersion of asbestos fibre, thatis responsive to electrophoresis between a cathode and an anode,applying an electric potential difference across said cathode and anode,whereby solid constituents are caused to migrate towards the anode,collecting the migrating constituents as a deposit, and continuouslyremoving the deposit from the remainder of the dispersion.

2. A process as claimed in claim 1 in which the deposit is formed on theanode and is continuously stripped off it as a coherent body.

3. A process as claimed in claim 1 in which a binder is deposited withthe asbestos.

4. A process as claimed in claim 3 in which the dispersion contains awater-soluble soap as a dispersing agent and the anode is of a metalwhich corrodes during the process, whereby metal ions are dissolved fromthe anode and combine with the soap to form a water-insoluble soap asthe binder.

5. A process as claimed in claim 1 in which the anode is continuouslymoved through and out of the dispersion.

6. A process as claimed in claim 1 in which the deposit is formed as asheet or tape on a plate anode, the sides of the anode being shieldedfrom the dispersion.

7. A process as claimed in claim 1 in which the asbestos dispersioncontains other dispersedparticles carrying electric charges such thatthey undergo electrophoresis and are deposited with the asbestosparticles.

8. A process as claimed in claim 7 in which the dispersed particles arepolymer particles.

9. A process as claimed in claim 1 in which the disersion containsadditional fibres which are entrained by and codeposited with thedispersed asbestos.

10. A process as claimed in claim 1 in which the deposit is formed on anion-permeable membrane interposed in the path of the migratingconstituents to the anode.

References Cited UNITED STATES PATENTS 1,884,110 10/1932 Morehouse204-181 2,214,876 9/1940 Clark 2041 2,421,652 6/1947 Robinson et al.117--128.4 2,900,320 8/1959 Metcalfe et a1. 204300 JOHN H. MACK, PrimaryExaminer.

A. C. PRESCOTT, Assistant Examiner.

US. Cl. X.R. 20418l

1. A PROCESS FOR THE PRODUCTION OF AN ABESTOS PRODUCT COMPRISING THESTEPS OF PASSING AN ANIONIC AQUEOUS DISPERSION OF ASBESTOS FIBRE, THATIS RESPONSIVE TO ELECTROPHORESIS BETWEEN A CATHODE AND AN ANODE,APPLYING AN ELECTRIC POTENTIAL DIFFERENCE ACROSS SAID CATHODE AND ANODE,WHEREBY SOLID CONSTITUENTS ARE CAUSED TO MIGRATE TOWARDS THE ANODE,COLLECTING THE MIGRATING CONSTITUENTS AS A DEPOSIT, AND CONTINUOUSLYREMOVING THE DEPOSIT FROM THE REMAINDER OF THE DISPERSION.